The present invention relates to a deceleration control apparatus of an internal combustion engine. More particularly, the present invention relates to a deceleration control apparatus of an internal combustion engine having a vacuum advance mechanism which advances the ignition timing of the engine during idling.
In a conventional internal combustion engine, when the throttle valve closes to its idle position, the air-fuel mixture supplied to a combustion chamber becomes rich and will not burn completely. As a result, large amounts of hydrocarbon (HC) are emitted from the engine at that time.
A deceleration control device, for example, a throttle positioner system, which holds the throttle valve open slightly more than at the idle position when the engine is decelerating, causes the air-fuel mixture to become leaner, so that complete combustion of the mixture takes place. This device is known and utilized for reducing HC emission of various internal combustion engines.
In these various engines having a deceleration control device, some engines have an idle vacuum advance device, which operates only during a specific operating condition where the degree of the opening of the throttle valve is less than a predetermined value, and advances the ignition timing of the engine in accordance with the vacuum level in an intake passage downstream of the throttle valve, so as to reduce fuel consumption when the engine is idling.
However, such engines having both a deceleration control device and an idle vacuum advance device have other problems. During the decelerating operation, since the idle vacuum advance device operates and thus causes the ignition timing to advance considerably, HC emission increases in large quantities at that time in spite of the operation of the deceleration control device. Furthermore, since the ignition timing advances during deceleration, this reduces the effect of the engine braking operation.